The present invention is directed to integrated circuits and their processing for the manufacture of semiconductor devices. More particularly, the invention provides a method and device for patterning films of PCMO (Pr0.7Ca0.3MnO3) using an etching process. Merely by way of example, the invention has been applied to a resistive material for resistance random access memory (RRAM) devices. But it would be recognized that the invention has a much broader range of applicability. For example, the invention can be applied to microprocessor devices, memory devices, and application specific integrated circuit devices.
Integrated circuits or “ICs” have evolved from a handful of interconnected devices fabricated on a single chip of silicon to millions of devices. Current ICs provide performance and complexity far beyond what was originally imagined. In order to achieve improvements in complexity and circuit density (i.e., the number of devices capable of being packed onto a given chip area), the size of the smallest device feature, also known as the device “geometry”, has become smaller with each generation of ICs. Semiconductor devices are now being fabricated with features less than a quarter of a micron across.
Increasing circuit density has not only improved the complexity and performance of ICs but has also provided lower cost parts to the consumer. An IC fabrication facility can cost hundreds of millions, or even billions, of dollars. Each fabrication facility will have a certain throughput of wafers, and each wafer will have a certain number of ICs on it. Therefore, by making the individual devices of an IC smaller, more devices may be fabricated on each wafer, thus increasing the output of the fabrication facility. Making devices smaller is very challenging, as each process used in IC fabrication has a limit. That is to say, a given process typically only works down to a certain feature size, and then either the process or the device layout needs to be changed. An example of such a limit is the ability to pattern certain materials for memory devices. These materials include PCMO, which has been proposed for RRAM devices.
As background information, PCMO materials have been known. A large electric-pulse-induced reversible resistance change active at room temperature and under zero magnetic field has been discovered in colossal magnetoresistive (CMR) Pr0.7Ca0.3MnO3 thin films. Electric field-direction-dependent resistance changes of more than 1700% were observed under applied pulses of 100 ns duration and as low as 6.5 V magnitude. This electrically induced effect, observed in CMR materials at room temperature has both the benefit of a discovery in materials properties and the promise of applications for thin film manganites in the electronics arena including high-density nonvolatile memory. In conventional NiFe-based giant magnetoresistance materials, the patterning is generally performed by ion beam milling because of the relatively low volatility of metal halide etch products. It was reported that Cl2/Ar discharges operated under high density plasma conditions can provide practical etch rates for NiFe and related materials. Unfortunately, limited work has been performed in the CMR materials. It is considered difficult to etch the thin film of PCMO because of non-volatility of etch byproducts from Pr, Ca, and Mn, and possibly others. Ion mill can not provide enough mask selectivity which will be a serious concern as the device size continues to shrink beyond 0.13 um technology.
It has long been known that bulk ceramic and single-crystal specimens of hole-doped manganites of the basic perovskite structure La1-xMxMnO3 (where M is typically Ba, Sr, Ca, or Pb) display a large magnetoresistance (MR). The subsequent discovery of a large room temperature MR in thin films of doped manganate perovskite opened up the possibility of applications in read heads for hard disk drives, sensors and magnetic random access memories (MRAM). This was followed by the reports of a very large negative MR at 77K in thin film La0.67Ca0.33MnO3, termed colossal magnetoresistance (CMR). Conventional efforts have been focused on obtaining high MR ratios at lower magnetic fields than in the original reports and at higher temperatures. Chemical substitution on the trivalent site is observed to improve MR behavior, since interatomic distance influences the magnetic-exchange interactions between the cations. Therefore, Nd- and Pr-based manganites are expected to show improved MR behavior relative to La-based compounds. In addition large MR values have been achieved in LaMMnO3/SrTiO3/LaMMnO3 trilayers (M=Ca or Sr) at low fields. To fabricate spin-valve read heads or MRAM elements it is necessary to develop pattern transfer processes for the manganites. In conventional NiFe-based giant magnetoresistance materials, the patterning is generally performed by ion beam milling because of the relatively low volatility of metal halide etch products. In LaCaMnO3, they found that iodine and bromine plasma chemistries proved some degree of chemical enhancement in the etch mechanism. These and other limitations of conventional fabrication techniques can be found throughout the present specification and more particularly below.
From the above, it is seen that an improved technique for processing semiconductor devices is desired.